Reaching the vault | 18: Demon's Den DMC: Devil May Cry Guide

At the very beginning turn around and search a small area (screen above). Here you find a Small Vital Star. Only now enter a hall with great vault's door and listen what Vergil has to talk. Remember where the nearby Divinity Statue is, because you'll be returning here a lot.

Your main task is to restart four backup generators. Every of them is in unique area, to which a proper tunnel leads. I recommend to search them clockwise. Begin from the generator nr 1 (screen above).